1. Field of the Invention
The present invention relates generally to hip arthroplasty and pertains, more specifically, to apparatus and method for conducting interoperative trialing to determine an appropriate head offset and neck length in the femoral component of a prosthetic hip joint.
2. Description of the Related Prior Art
Total hip arthroplasty requires the preparation of an implant site for the reception of a femoral component and an acetabular component of a prosthetic hip joint to be implanted at the implant site. Proper hip mechanics are achieved through the selection of an appropriate head offset and neck length in the femoral component of the prosthetic hip implant. That is, the distance between the stem of the femoral component and the femoral head of the component, provided by the length of the neck of the component, establishes the requisite head offset and neck length which, in turn, provides the desired range of motion, leg length, and tension in the soft tissue at the implant site. Accordingly, of utmost importance is the ability to determine the appropriate neck length with precision, and to do so with ease and assurance.
The appropriate length required for the neck of a femoral component is determined once the size of each of the femoral component and the acetabular component is selected, and the implant site is prepared for the reception of each selected component. A preliminary assessment can be made utilizing radiographic analysis; however, a final determination usually is accomplished during the course of the implant procedure itself, that is, interoperatively.
In a current trialing procedure, serial trial prostheses are used to determine the appropriate neck length during the conduct of total hip arthroplasty. Thus, a provisional trial prosthesis is put into place, the hip joint is reduced, and the leg of the patient is moved by a surgeon through a range of motion to determine hip mechanics by hand. The trialing procedure requires that the trial prosthesis be removed and replaced with another in a series of trial prostheses in order to evaluate the effect of different neck lengths on hip mechanics. To achieve correct hip mechanics, a surgeon may need to perform several iterations, each requiring replacement of one trial prosthesis with another in the series, reduction of the hip joint, movement through a range of motion, and then dislocation of the joint again in order to change trials. The procedure can be quite time-consuming and even physically challenging, especially with larger patients. Moreover, the procedure is not suited to the conduct of more recently developed minimally invasive total hip arthroplasty where access to the hip joint is more limited.